The present invention relates to a fuel control method for a gasoline engine, and more particularly, to a fuel control method that employs air/fuel ratio matching coefficients to decrease the difference between the air/fuel ratios of a first cylinder bank and a second cylinder bank.
There have been many attempts to increase engine output torque and decrease emission gases through engine fuel control. These have resulted in the development of an oxygen sensor for feedback control of the air/fuel ratio. To control the ratio, the oxygen sensor is disposed in the exhaust system of the engine. It detects the oxygen concentration in the exhaust gas. Signals from the oxygen sensor are used to maintain the air/fuel ratio near a stoichiometric value (14.7:1) through feedback control.
The air/fuel ratio is determined by engine operating conditions. For precise control of the air/fuel ratio, many control steps are needed for achieving and maintaining the stoichiometric value.
The air/fuel ratio is mainly determined by the amount of air and fuel. An initial amount of fuel is determined based on an amount of air drawn into the engine, as determined by a conventional mass air flow sensor. After setting the initial amount of fuel based on various operating conditions, such as different coolant temperatures, intake air temperatures, amounts of purge fuel, throttle openings, and engine speeds, etc., a final amount of fuel is determined. Also, the air/fuel ratio is modified through a feedback control loop than uses signals of the oxygen sensor to maintain the air/fuel ratio near the stoichiometric value.
This feedback control is performed under certain specific conditions. If the conditions control do not exist, the air/fuel ratio cannot be maintained to be near the stoichiometric value. And if the air/fuel ratio is far from the stoichiometric value, that is, if the air/fuel ratio is considerably lean or rich, noxious emission gases greatly increase.
To guard against increased emissions, the initial amount of fuel is modified using an air/fuel ratio matching coefficient. The air/fuel ratio matching coefficient is determined so that the air/fuel ratio is maintained to be near the stoichiometric value. That is, an amount of fuel is modified by multiplying the initial amount of fuel by the air/fuel ratio matching coefficient. The resultant air/fuel ratio using the modified amount of fuel is nearer the stoichiometric value.
The air/fuel ratio matching coefficient is preferably determined by engine speed and volumetric efficiency. The volumetric efficiency (%) is a ratio of an amount of air drawn into an engine with respect to a volume of a cylinder, under standard atmospheric pressure.
The air/fuel ratio matching coefficients for various combinations of engine speed and volumetric efficiency are experimentally determined and stored in a memory that is accessible by a controller. The controller applies the air/fuel ratio matching coefficient to the air/fuel ratio control for a particular engine speed. Thus, even when feedback control of the air/fuel cannot be performed, the air/fuel ratio may be maintained to be near the stoichiometric value.
In a V-6 engine having a first cylinder bank and a second cylinder bank, the air/fuel ratio matching coefficient is also used for the air/fuel ratio control. In conventional air/fuel ratio control, a common air/fuel ratio matching coefficient is applied to both banks, i.e., at a specific engine speed and volumetric efficiency, one air/fuel ratio matching coefficient is applied to both banks.
But, in an engine having a first bank and a second bank, amounts of air drawn into the first bank and the second bank are different because of the differences between the shapes of parts of the intake systems connected to the first and second banks. Therefore, if amounts of fuel are equal in both first and second banks, the air/fuel ratios of the first bank and the second bank are different, that is, the air/fuel ratio of one of the banks may be lean, while that of the other is rich.
In a preferred embodiment of the present invention, a fuel control method for an internal combustion engine comprises: detecting an amount of intake air; determining a basic (or initial) amount of fuel based on the detected amount of intake air; detecting an engine speed; calculating a volumetric efficiency based on the detected amount of intake air; determining a first cylinder bank air/fuel ratio matching coefficient and a second cylinder bank air/fuel ratio matching coefficient at the detected engine speed and the detected volumetric efficiency; and determining a final amount of fuel for the first bank based on the initial amount of fuel and the first bank air/fuel ratio matching coefficient; and determining a final amount of fuel for the second bank based on the initial amount of fuel and the second bank air/fuel ratio matching coefficient.
Preferably, the first bank air/fuel ratio matching coefficient and the second bank air/fuel ratio matching coefficient are determined such that both air/fuel ratios of the first bank and the second bank are maintained to be near a stoichiometric air/fuel ratio value at every engine speed and volumetric efficiency.
In a preferred embodiment of the present invention, the determining an amount of fuel comprises: determining that a current fuel control mode is not an air/fuel ratio feedback control mode; and determining an amount of fuel (TCONTROL) according to the following equation:   TCONTROL  =            TB      xc3x97              (                  KLRN          +          KFB                )            xc3x97      KMTCH_NEW      xc3x97      KWUP      xc3x97      KAFND      xc3x97      KPRGLEAN      xc3x97              (                  1          +          KAS                )              +          [              xe2x80x83            ⁢                                                  T              ACL                                                            0                                                              T              DCL                                          ]      
In an additional preferred embodiment of the invention the determination that the fuel control mode is not the air/fuel ratio feedback control mode is made based on a coolant temperature signal and an oxygen sensor signal.
In another preferred embodiment of the present invention, the fuel control system for an internal combustion engine including an first cylinder bank and a second cylinder bank comprises: a control unit for determining an amount of fuel based on one or more engine operating conditions and generating a signal representative of the determined amount of fuel; and a fuel injection device for injecting fuel into the engine according to the signal of the control unit. Preferably, the control unit is programmed to execute a control method comprising: detecting an amount of intake air; determining an initial amount of fuel based on an amount of intake air; detecting an engine speed; calculating a volumetric efficiency based on the detected amount of intake air and engine speed; determining a first bank air/fuel ratio matching coefficient and a second bank air/fuel ratio matching coefficient for the detected engine speed and the volumetric efficiency; determining a final amount of fuel for the first bank based on the initial amount of fuel and the first bank air/fuel ratio matching coefficient; and determining a final amount of fuel for the second bank based on the initial amount of fuel and the second bank air/fuel ratio matching coefficient.
Preferably, the first bank air/fuel ratio matching coefficient and the second bank air/fuel ratio matching coefficient are determined so that both air/fuel ratios of the first bank and the second bank are maintained to be substantially near a stoichiometric air/fuel ratio value at every engine speed and volumetric efficiency. This may be accomplished by modifying the initial amount of fuel with the first bank air/fuel ratio matching coefficient and the second bank air/fuel ratio matching coefficient.